1. Field of the Invention
The present invention relates to a use of a stem cell conditioned medium to inhibit melanin formation for skin whitening, in which the conditioned medium obtained from human Wharton's jelly-derived mesenchymal stem cells (WJMSCs) conditioned basal medium can effectively decrease tyrosinase activity and inhibit melanin formation in skin cells so as to achieve efficacy of skin whitening.
2. Description of Related Art
In mammals such as humans, skin is the soft outer covering all over a mammal body and enables to interface with the environment as the first line of defense from external factors. Therefore, skin is the most vulnerable organ to external stimuli and UV damage. In order to protect skin, melanocytes synthesize melanin to resist UV radiation. Melanin, a kind of biological pigments, is derived from tyrosine by a series of chemical reactions. In melanocytes, tyrosine is catalyzed by tyrosinase to form dihydroxyphenylalanine (Dopa), and Dopa is converted to Dopaquinone by dehydrogenation. Two other enzymes, tyrosinase-related protein 1 (TRP1) and tyrosinase-related protein 2 (TRP2) are also shown to participate in this processes to synthesize the final product of eu-melanin. Furthermore, when a skin is exposed to UV radiation, a small amounts of free radicals will be produced and thus activate signaling pathways to stimulate transcription of tyrosinase in the skin, resulting in an increased synthesis of melanin and causing the freckles formation. If people don't timely care their skin after UV radiation, increasing freckles will make the skin look dull.
Nowadays, various ingredients are identified to have whitening effects, including arbutin, acelaic acid, kojic acid, hydroquinone and the like. However, some limitations and side effects are existed, e.g. kojic acid may cause liver cancer, and hydroquinone is relatively unstable and has the potential to damage the melanocyte. Moreover, some whitening agents applied on users' skin may also cause the phenomenon of allergy, redness and discomfort. Therefore, it is necessary to develop a safer and more effective whitening ingredient.
In these years, studies of stem cells have been a growing trend in the world. Stem cells can mainly be divided into two categories, embryonic stem cells and adult stem cells. Mesenchymal stem cells (MSCs) belong to adult stem cells and have a great potential for differentiation. MSCs can differentiate into not only tissues (such as skeleton) derived from mesoderm, but also visceral cells (such as liver and pancreas) derived from endoderm and neurons derived from ectoderm. MSCs are ubiquitous in adults' bodies and can be isolated from bone marrows and various organs. However, the number of MSCs in the bodies is small, and adults' MSCs are known to gradually decrease with the age of the donors. Therefore, how to obtain a sufficient amount of MSCs becomes very important. Bone marrow MSCs are mainly derived from adult bone marrow, but invasive ways to get the bone marrow MSCs may cause pain and discomfort to donors. Umbilical cords contain a number of rich and young MSCs with strong differentiation potential, so they can be used as an important source of mesenchymal stem cells. In comparison with obtaining MSCs from bone marrows, obtaining MSCs from umbilical cords is relatively easy. Moreover, recent studies showed that adipose-derived stem cells-conditioned medium (ADSC-CM) have inhibitory effects on melanin synthesis in melanoma B16 cells (Biol. Pharm. Bull. 31(4) 606-610, 2008). The conditioned medium effectively achieves whitening effects by down-regulating the expression of tyrosinase and tyrosinase-related protein 1 (TRP1).